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                                <h2 id="54--stringbuffer&#x7C7B;">5.4  StringBuffer&#x7C7B;</h2>
<h3 id="541--stringbuffer&#x7C7B;&#x7684;&#x6982;&#x5FF5;">5.4.1  StringBuffer&#x7C7B;&#x7684;&#x6982;&#x5FF5;</h3>
<p>&#x2003;&#x2003;StringBuffer&#x7C7B;&#x4E5F;&#x53EF;&#x4EE5;&#x5B58;&#x653E;&#x5B57;&#x7B26;&#x4E32;&#x3002;&#x4E0E;String&#x7C7B;&#x4E0D;&#x540C;&#x7684;&#x662F;&#xFF0C;StringBuffer&#x5B57;&#x7B26;&#x4E32;&#x4EE3;&#x8868;&#x7684;&#x662F;&#x53EF;&#x53D8;&#x7684;&#x5B57;&#x7B26;&#x5E8F;&#x5217;&#xFF0C;&#x53EF;&#x4EE5;&#x5BF9;&#x5B57;&#x7B26;&#x4E32;&#x5BF9;&#x8C61;&#x7684;&#x5185;&#x5BB9;&#x8FDB;&#x884C;&#x4FEE;&#x6539;&#x3002; </p>
<p>&#x2003;&#x2003;&#x4EE5;&#x4E0B;&#x662F;StringBuffer&#x7C7B;&#x6700;&#x5E38;&#x7528;&#x7684;&#x6784;&#x9020;&#x65B9;&#x6CD5;&#x3002;</p>
<ul>
<li><p>StringBuffer()&#xFF1A;&#x6784;&#x9020;&#x4E00;&#x4E2A;&#x5176;&#x4E2D;&#x4E0D;&#x5E26;&#x5B57;&#x7B26;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x7F13;&#x51B2;&#x533A;&#xFF0C;&#x5176;&#x521D;&#x59CB;&#x5BB9;&#x91CF;&#x4E3A;16&#x4E2A;&#x5B57;&#x7B26;&#x3002;</p>
</li>
<li><p>StringBuffer(String str)&#xFF1A;&#x6784;&#x9020;&#x4E00;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x7F13;&#x51B2;&#x533A;&#xFF0C;&#x5E76;&#x5C06;&#x5176;&#x5185;&#x5BB9;&#x521D;&#x59CB;&#x5316;&#x4E3A;&#x6307;&#x5B9A;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x5185;&#x5BB9;&#x3002;</p>
</li>
</ul>
<p>&#x2003;&#x2003;StringBuffer&#x5B57;&#x7B26;&#x4E32;&#x4F7F;&#x7528;&#x573A;&#x5408;&#x4E3A;&#x7ECF;&#x5E38;&#x9700;&#x8981;&#x5BF9;&#x5B57;&#x7B26;&#x4E32;&#x5185;&#x5BB9;&#x8FDB;&#x884C;&#x4FEE;&#x6539;&#x64CD;&#x4F5C;&#x7684;&#x573A;&#x5408;&#x3002;</p>
<h3 id="542--stringbuffer&#x7C7B;&#x7684;&#x4F7F;&#x7528;">5.4.2  StringBuffer&#x7C7B;&#x7684;&#x4F7F;&#x7528;</h3>
<p>&#x2003;&#x2003;&#x4EE5;&#x4E0B;&#x662F;&#x901A;&#x8FC7;StringBuffer&#x7C7B;&#x7684;&#x6784;&#x9020;&#x65B9;&#x6CD5;&#x521B;&#x5EFA;StringBuffer&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x4EE3;&#x7801;&#x3002;</p>
<pre><code>StringBuffer strB1 = new StringBuffer();
</code></pre><p>&#x2003;&#x2003;&#x901A;&#x8FC7;strB1.length()&#x8FD4;&#x56DE;&#x957F;&#x5EA6;&#x662F;0&#xFF0C;&#x4F46;&#x5728;&#x5E95;&#x5C42;&#x521B;&#x5EFA;&#x4E86;&#x4E00;&#x4E2A;&#x957F;&#x5EA6;&#x4E3A;16&#x7684;&#x5B57;&#x7B26;&#x6570;&#x7EC4;&#x3002;</p>
<pre><code>StringBuffer strB2 = new StringBuffer(&quot;&#x67F3;&#x6D77;&#x9F99;&quot;);
</code></pre><p>&#x2003;&#x2003;&#x901A;&#x8FC7;strB2.length()&#x8FD4;&#x56DE;&#x957F;&#x5EA6;&#x662F;3&#xFF0C;&#x5728;&#x5E95;&#x5C42;&#x521B;&#x5EFA;&#x4E86;&#x4E00;&#x4E2A;&#x957F;&#x5EA6;&#x4E3A;3+16&#x7684;&#x5B57;&#x7B26;&#x6570;&#x7EC4;&#x3002;</p>
<p>&#x2003;&#x2003;StringBuffer&#x4E0A;&#x7684;&#x4E3B;&#x8981;&#x64CD;&#x4F5C;&#x662F;append&#x548C;insert&#x65B9;&#x6CD5;&#xFF0C;&#x5C06;&#x5B57;&#x7B26;&#x8FFD;&#x52A0;&#x6216;&#x63D2;&#x5165;&#x5230;&#x5B57;&#x7B26;&#x4E32;&#x7F13;&#x51B2;&#x533A;&#x4E2D;&#x3002;append&#x65B9;&#x6CD5;&#x59CB;&#x7EC8;&#x5C06;&#x5B57;&#x7B26;&#x6DFB;&#x52A0;&#x5230;&#x7F13;&#x51B2;&#x533A;&#x7684;&#x672B;&#x7AEF;&#xFF0C;&#x800C;insert&#x65B9;&#x6CD5;&#x5219;&#x5728;&#x6307;&#x5B9A;&#x7684;&#x4F4D;&#x7F6E;&#x6DFB;&#x52A0;&#x5B57;&#x7B26;&#x3002;</p>
<p>&#x2003;&#x2003;&#x4EE5;&#x4E0B;&#x662F;StringBuffer&#x7C7B;&#x7684;&#x5E38;&#x7528;&#x65B9;&#x6CD5;&#x3002;</p>
<ul>
<li>public StringBuffer append(String str)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;&#x6307;&#x5B9A;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5B57;&#x7B26;&#x5E8F;&#x5217;&#x4E2D;&#x3002;</p>
<ul>
<li>public StringBuffer append(StringBuffer str)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;&#x6307;&#x5B9A;&#x7684;StringBuffer&#x5B57;&#x7B26;&#x4E32;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5E8F;&#x5217;&#x4E2D;&#x3002;</p>
<ul>
<li>public StringBuffer append(char[] str)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;&#x5B57;&#x7B26;&#x6570;&#x7EC4;&#x53C2;&#x6570;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x8868;&#x793A;&#x5F62;&#x5F0F;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5E8F;&#x5217;&#x4E2D;&#x3002;</p>
<ul>
<li>public StringBuffer append(char[] str,int offset,int len)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;&#x5B57;&#x7B26;&#x6570;&#x7EC4;&#x53C2;&#x6570;&#x7684;&#x5B50;&#x6570;&#x7EC4;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x8868;&#x793A;&#x5F62;&#x5F0F;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5E8F;&#x5217;&#x4E2D;&#xFF0C;&#x4ECE;&#x7D22;&#x5F15;offset&#x5F00;&#x59CB;&#xFF0C;&#x6B64;&#x5B57;&#x7B26;&#x5E8F;&#x5217;&#x7684;&#x957F;&#x5EA6;&#x5C06;&#x589E;&#x52A0;len&#x3002;</p>
<ul>
<li>public StringBuffer append(double d)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;double&#x7C7B;&#x578B;&#x53C2;&#x6570;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x8868;&#x793A;&#x5F62;&#x5F0F;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5E8F;&#x5217;&#x4E2D;&#x3002;</p>
<ul>
<li>public StringBuffer append(Object obj)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;Object&#x53C2;&#x6570;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x8868;&#x793A;&#x5F62;&#x5F0F;&#x8FFD;&#x52A0;&#x5230;&#x6B64;&#x5E8F;&#x5217;&#x4E2D;&#x3002;</p>
<ul>
<li>public StringBuffer insert(int offset,String str)</li>
</ul>
<p>&#x2003;&#x2003;&#x5C06;&#x5B57;&#x7B26;&#x4E32;&#x63D2;&#x5165;&#x5230;&#x6B64;&#x5B57;&#x7B26;&#x5E8F;&#x5217;&#x4E2D;&#xFF0C;offset&#x8868;&#x793A;&#x63D2;&#x5165;&#x4F4D;&#x7F6E;&#x3002;</p>
<p>&#x2003;&#x2003;&#x4E0B;&#x9762;&#x901A;&#x8FC7;&#x4E00;&#x4E2A;&#x6848;&#x4F8B;&#x8BF4;&#x660E;&#x4E0A;&#x8FF0;StringBuffer&#x7C7B;&#x65B9;&#x6CD5;&#x7684;&#x4F7F;&#x7528;&#xFF0C;&#x6267;&#x884C;&#x4E0B;&#x9762;&#x7684;&#x7A0B;&#x5E8F;&#xFF0C;&#x8FD0;&#x884C;&#x7ED3;&#x679C;&#x5982;&#x56FE;5.16&#x6240;&#x793A;&#x3002;</p>
<pre><code>public class TestStringBuffer {

    public static void main(String[] args) {            

        System.out.println(&quot;&#x521B;&#x5EFA;StringBuffer&#x5BF9;&#x8C61;&quot;);

        //&#x4F7F;&#x7528;StringBuffer()&#x6784;&#x9020;&#x5668;&#x521B;&#x5EFA;&#x5BF9;&#x8C61;

        StringBuffer strB1 = new StringBuffer();

        System.out.println(&quot;new StringBuffer()&#x521B;&#x5EFA;&#x5BF9;&#x8C61;&#x7684;&#x957F;&#x5EA6;&#x4E3A;&#xFF1A;&quot; + strB1.length());

        //&#x4F7F;&#x7528;StringBuffer(String str)&#x6784;&#x9020;&#x5668;&#x521B;&#x5EFA;&#x5BF9;&#x8C61;

        StringBuffer strB2 = new StringBuffer(&quot;&#x67F3;&#x6D77;&#x9F99;&quot;);            

        System.out.println(&quot;new StringBuffer(\&quot;&#x67F3;&#x6D77;&#x9F99;\&quot;)&#x521B;&#x5EFA;&#x5BF9;&#x8C61;&#x7684;&#x957F;&#x5EA6;&#x4E3A;&#xFF1A;&quot; + strB2.length());

        System.out.println(&quot;strB2&#x91CC;&#x7684;&#x5185;&#x5BB9;&#x4E3A;&#xFF1A;&quot; + strB2);

        //&#x4F7F;&#x7528;append&#x3001;insert&#x65B9;&#x6CD5;&#x8FFD;&#x52A0;&#x3001;&#x63D2;&#x5165;&#x5B57;&#x7B26;&#x4E32;

        System.out.println(&quot;&#x4F7F;&#x7528;append&#x65B9;&#x6CD5;&#x8FFD;&#x52A0;&#x5B57;&#x7B26;&#x4E32;&quot;);

        strB2.append(&quot;&#xFF0C;&#x60A8;&#x597D;&#xFF01;&quot;);            //&#x5728;&#x6700;&#x540E;&#x589E;&#x52A0;&quot;&#xFF0C;&#x60A8;&#x597D;&quot;&#xFF01;

        System.out.println(strB2);

        strB2.insert(3,&quot;&#x5DE5;&#x7A0B;&#x5E08;&quot;);               //&#x4ECE;&#x7B2C;4&#x4E2A;&#x4F4D;&#x7F6E;&#x5F00;&#x59CB;&#xFF0C;&#x63D2;&#x5165;&quot;&#x5DE5;&#x7A0B;&#x5E08;&quot;

        System.out.println(strB2);

    }

}
</code></pre><center><img src="https://labfile.oss.aliyuncs.com/library/textbook-java1/img/d5z/tu5.16.png"></center>
<center> &#x56FE;5.16  StringBuffer&#x5E38;&#x7528;&#x65B9;&#x6CD5;</center>  
### 5.4.3  StringBuffer&#x5185;&#x5B58;&#x6A21;&#x578B;  

&#x2003;&#x2003;StringBuffer&#x662F;&#x4E00;&#x4E2A;&#x5185;&#x5BB9;&#x53EF;&#x53D8;&#x7684;&#x5B57;&#x7B26;&#x5E8F;&#x5217;&#xFF0C;&#x6216;&#x8005;&#x8BF4;&#x5B83;&#x662F;&#x4E00;&#x4E2A;&#x5185;&#x5BB9;&#x53EF;&#x53D8;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x7C7B;&#x578B;&#x3002;&#x5F53;&#x4F7F;&#x7528;StringBuffer strB1 = new StringBuffer(&quot;&#x67F3;&#x6D77;&#x9F99;&quot;);&#x8BED;&#x53E5;&#x521B;&#x5EFA;StringBuffer&#x5BF9;&#x8C61;&#x65F6;&#xFF0C;&#x5185;&#x5B58;&#x7ED3;&#x6784;&#x793A;&#x610F;&#x56FE;&#x5982;&#x56FE;5.17&#x6240;&#x793A;&#x3002;

<center><img src="https://labfile.oss.aliyuncs.com/library/textbook-java1/img/d5z/tu5.17.png"></center>
<center>&#x56FE;5.17  StringBuffer&#x5185;&#x5B58;&#x7ED3;&#x6784;&#x793A;&#x610F;&#x56FE;&#x4E00;</center>  

<p>&#x2003;&#x2003;&#x5F53;&#x4F7F;&#x7528;strB1.append(&quot;&#x5DE5;&#x7A0B;&#x5E08;&quot;)&#x65B9;&#x6CD5;&#x65F6;&#xFF0C;&#x5C06;&#x4E4B;&#x524D;&#x521B;&#x5EFA;&#x7684;StringBuffer&#x5BF9;&#x8C61;&#x7684;&#x5185;&#x5BB9;&#x201C;&#x67F3;&#x6D77;&#x9F99;&#x201D;&#x4FEE;&#x6539;&#x6210;&#x201C;&#x67F3;&#x6D77;&#x9F99;&#x5DE5;&#x7A0B;&#x5E08;&#x201D;&#xFF0C;&#x5185;&#x5B58;&#x7ED3;&#x6784;&#x793A;&#x610F;&#x56FE;&#x5982;&#x56FE;5.18&#x6240;&#x793A;&#x3002;</p>
<center><img src="https://labfile.oss.aliyuncs.com/library/textbook-java1/img/d5z/tu5.18.png"></center>
<center> &#x56FE;5.18  StringBuffer&#x5185;&#x5B58;&#x7ED3;&#x6784;&#x793A;&#x610F;&#x56FE;&#x4E8C; </center>  




                                
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